is it possible to rotate your computer setup so it faces away from the door?
and also have something to tab out onto as appose to your desktop like a game or a non mlp music video 

Why are you keeping it a secret?

If you want to be extremely incognito about it, you probably should get different wallpapers. :3

But, if you think you should tell your parents about it, do. Just say you watch a show named My Little Pony: Friendship is Magic and you think it's pretty good.

Everything else you do will be up to you. I haven't revealed myself to my parents yet either: just a couple of IRL friends and they don't really care.

That's kind of how it started for me: Changing my desktop wallpaper to an image of Rainbow Dash sleeping on a cloud.  My mom saw the wallpaper and thought it was cute; maybe yours will, too.